The present invention relates to polyamide-containing ligands covalently bonded to inorganic and organic solid supports and methods of using the same for removing, separating and concentrating certain desired metal ions from solutions, even when the desired ions are in the presence of other metal ions and/or hydrogen ions at much higher concentrations.
Effective methods for the separation and recovery of particular ions such as the transition, post-transition and alkaline earth metal ions from solution mixtures containing these and other metal ions are of great importance in modern technology. Particularly, it is difficult to separate and recover certain metal ions such as Cd2+, Pb2+, Ag+, Ni2xe2x88x92, Co2+, Fe3+, Cu2+, Sr2xe2x88x92, and/or Ca2+ from the presence of even moderate amounts of hydrogen ion (H+). It is also very difficult to remove the mentioned desired metal ions when present at low concentrations in solutions that contain other, non-desirable metal ions at much greater concentrations. Thus, there is a real need for a composition of matter and an associated method that may be used for selectively separating certain transition, post-transition, and alkaline earth metal ions from other non-desirable ions.
It is known that ethylenediaminetetraacetamide (EDTAA), diethylenetriaminepentaacetamide (DTPAA), and nitrilotriacetamide (NTAA) form strong complexes with various metal ions in solution. These molecules may be shown as Formulas 1-3 respectively below: 
J. M. Grana-Molares, C. Baluja-Santos, A. Alvarez-Devesa and F. Bermejo-Martinez, Etude Spectrophotometrique des Complexes du Cobalt(III) avec les Amides de l""EDTA et du DTPA, Analysis, Volume 7, 249-252 (1979) (report on the synthesis of EDTAA and DTPAA and their ability to complex Co(III) as shown by a spectrophotometric technique). In a different study, L. Przyborowski showed that NTAA and EDTAA could be prepared by modifying known methods and that Cu(II) formed strong complexes with NTAA. L. Przyborowski, Complex Compounds of Amides and Thioamides of Aminopolycarboxylic Acids, Part III. Synthesis, Properties and Copper(II) Complexes of Nitrilotriacetotriamide and Ethylenediaminetetraacetotetraamide, Roczniki Chemii, Volume 44, 1883-1893 (1970).
More recently, a great deal of research has been done in the synthesis and metal ion complexation properties of polyamide-containing azacrown ethers such as those containing acetamide, propionamide, and peptide side arms. R. Kataky, K. E. Matthes, P. E. Nicholson, D. Parker and H-J. Buschmann, Synthesis and Binding Properties of Amide-Functionalized Polyazamacrocycles, Journal of the Chemical Society, Perkin Transactions 2, 1425-1432 (1990) (reported on the synthesis and complexation properties of per-N-(dimethylacetamido)-substituted triaza-9-crown-3, aza-12-crown-4, diaza-12-crown-4, and tetraaza-12-crown-4). The ligating agents 1,4,7,10-tetrakis(N,N-dimethylacetamido)-1,4,7,10-tetraazacyclododecane and 1,7-dioxo-4,10-bis(N,N-dimethylacetamido)-4,10-diazacyclododecane are two chemical structures that were synthesized and which are representative of polyamide-containing ligating agents of the present invention. These ligating agents are shown respectively below in Formulas 4 and 5: 
The diamide of Formula 5 was shown to form complexes with all of the alkali metal and alkaline earth metal cations. Further, this diamide was shown to have significant selectivity for Ca2+ over the other cations studied. However, a diamide similar to that of Formula 5, but containing one more methylene group in each amide-containing arm (thus, having two N,N-dimethylpropioamido substituents), was shown to form weaker complexes with these same metal ions.
Further studies of amide ligands such as those depicted by formulas 4 and 5 have concluded that the size of the metal ion-ligand chelate ring determines the strength of the interaction between the ligand and the metal ions. For example, a five-membered ring favored the smaller cations over a six-membered ring. Representative of fully chelated metals (Me) having five- and and six-membered amide rings attached are shown in Formulas 6 and 7 respectively below: 
H. Maumela, R. D. Hancock, L. Carlton, and J. H. Reibenspies and K. P. Wainwright, The Amide Oxygen as a Donor Group. Metal Ion Complexing Properties of Tetra-N-Acetamide Substituted Cyclen: A Crystallographic, NMR, Molecular Mechanics and Thermodynamic Study, Journal of the American Chemical Society, Volume 117, 6698-6707 (1995). Further, in this article, the authors reported the synthesis of 1,4,7,10-tetraazacyclododecane (DOTAM) which is the unsubstituted amide analogue of the tetraamide of Formula 4. DOTAM is capable of forming complexes with a host of metal ions including many transition and post-transition metal ions. DOTAM also forms strong complexes with Cd2+ and Pb2+, even at pH levels as low as 0.3 which is equivalent to a hydrogen ion concentration of 0.5 Molar. DOTAM may be represented by Formula 8 below: 
The articles cited above disclose procedures for synthesizing and demonstrating limited useful complexation properties of polyamide-containing ligand molecules. However, researchers have not previously been able to incorporate polyamide-containing ligands into solid phase separation systems. This is significant because polyamide-containing ligands present merely as a solute in solution act to complex selected ions, but provide no means for their separation. Specifically, never before have polyamide-containing ligands been successfully covalently bonded to porous and/or non-porous organic and/or inorganic solid supports. Therefore, it would be useful to provide a polyamide-containing ligand attached to a solid support so that these and other polyamide-containing ligands could be used to separate out desired metal ions.
The present invention is drawn to novel porous and/or non-porous particulate organic and/or inorganic solid supports covalently bonded to polyamide-containing ligands. When an inorganic solid support is used, the solid support is bonded to the polyamide-containing ligand through a covalent linkage mechanism and a hydrophilic spacer grouping. When the particulate solid support is an organic resin or polymer, the polyamide-containing ligand may be bonded directly to an activated polar group on the polymer through a covalent linkage mechanism.
The unique composition of matter of this invention comprises polyamide-containing ligands having three or more amide groups (NHC(O)CH2), two or more amine nitrogens separated by at least two carbons and at least one solid support linkage.
The invention is also drawn to the concentration and removal of certain desired divalent metal ions including transition, post-transition, and alkaline earth metal ions. The present invention is particularly useful for removing such ions as Cd2+, Pb2+, Ag+, Ni2+, Co2+, Fe3+, Cu2+, Sr2+, and/or Ca2+ from source solutions. This is true whether the desired ions are present at very low or very high concentrations, i.e., from ppb to g/l.
The concentration of desired ions is accomplished by forming a complex of desired ions with a polyamide-containing ligand covalently bound to a solid support material by flowing a source solution containing the desired ions through a column packed with polyamide-containing ligand bound solid support material. This process enables the desired ions to complex with the polyamide-containing ligand attached to the solid support. The metal ion and the polyamide-containing ligand are then decoupled by flowing a receiving liquid through the column (in much smaller volume than the volume of source solution passed through the column) to remove and concentrate the desired ions in the receiving liquid solution. The receiving liquid or recovery solution forms a stronger complex with the desired ions than does the polyamide-containing ligand, or alternatively, temporarily forms a stronger interaction with the polyamide-containing ligand than does the desired metal ions. In either case, the desired metal ions are quantitatively stripped from the ligand in a concentrated form in the receiving solution. The recovery of desired ions from the receiving liquid may be accomplished by various methods commonly known in the art including evaporation, electrowinning, and precipitation among others.
The compositions of the present invention comprise polyamide-containing ligands that are covalently bonded to an inorganic or organic solid support through a spacer and are represented by Formula 9 as follows:
SSxe2x80x94Axe2x80x94Xxe2x80x94Lxe2x80x83xe2x80x83Formula 9
wherein SS is a solid support, A is a covalent linkage mechanism, X is a hydrophilic spacer grouping, and L is a polyamide-containing ligand.
The SSxe2x80x94Axe2x80x94Xxe2x80x94 portion of Formula 9 is well known for use with ion binding ligands. Preferably, the solid support (SS) is an inorganic and/or organic particulate support material selected from the group consisting of silica, silica gel, silicates, zirconia, titania, alumina, nickel oxide, glass beads, phenolic resins, polystyrenes, and polyacrylates. However, other organic resins or any other hydrophilic organic and/or inorganic support materials meeting the above criteria can also be used.
The use of organic ion binding ligands attached to an Sxe2x80x94Axe2x80x94Xxe2x80x94 solid support by means of a covalent linkage spacer grouping is illustrated in U.S. Pat. Nos. 4,943,375; 4,952,321; 4,959,153; 4,960,882; 5,039,419; 5,071,819; 5,078,978; 5,084,430; 5,173,470; 5,179,213; 5,182,251; 5,190,661; 5,244,856; 5,273,660; and 5,393,892. These patents, which disclose various spacers that can be used in forming an organic ligand attached to a solid support, are incorporated herein by reference.
When the solid support (SS) is an inorganic material such as silica, silica gel, silicates, zirconia, titania, alumina, nickel oxide, or glass beads, the covalent linkage (A) is a silane such that Axe2x80x94X may be represented by Formula 10 as follows: 
where each Z is independently selected from the group consisting of Cl, Br, I, lower alkyl, lower alkoxy, substituted lower alkyl or substituted lower alkoxy and S (as used herein, lower alkyl or lower alkoxy means a group having 1 to 8 carbon atoms); and X is a spacer grouping represented by Formula 11 as follows:
xe2x80x83(CH2)a[OCH2CHR1CH2]bxe2x80x83xe2x80x83Formula 11
wherein R1 is a member selected from the group consisting of H, SH, OH, lower alkyl, and aryl; a is an integer from 2 to about 10; and b is 0 or 1. In Formula 11, the terminal carbon (or xe2x80x94CH2xe2x80x94 group most distal to the solid support) may attach to the polyamide-containing ligand by any suitable bond. However, it is preferred that the terminal carbon on the spacer be covalently bonded to a nitrogen or another carbon present on the ligand.
Often, the terminal carbon on the spacer (X) will bond to either the carbon or the nitrogen found on an amide group of the polyamide-containing ligand. For example, if the ligand has 4 amide groups, one may be used to attach the ligand to the spacer (X) leaving 3 amide groups available for complexing desired ions. If the terminal carbon on the spacer (X) is to bond to an amide group of the ligand (L), Formula 12 below is representative of such an amide group:
(NH)m(CH2)nC(O)(NH)n(CH2)mxe2x80x83xe2x80x83Formula 12
where m is 0 or 1; and n is 0 or 1 with the proviso that when m is 1, n is 0 and when m is 0, n is 1. Thus, the terminal carbon can either covalently bond to a nitrogen or a carbon atom of the amide group.
Conversely, the spacer (X) does not have to bond to an amide group at all. In some embodiments, the spacer (X) bonds directly to a nitrogen or carbon atom or other appropriate atom that is not part of an amide group. In other embodiments, the SSxe2x80x94Axe2x80x94Xxe2x80x94 portion will attach to the polyamide-containing ligand by replacing one of the amide groups. Therefore, the attachment of the spacer (X) to the polyamide-containing ligand (L) should be limited only by functionality.
When the particulate solid support (SS) is an organic resin or polymer, such as phenolic resins, polystyrenes, and polyacrylates, it will generally be a hydrophilic polymer or polymer derivatized to have a hydrophilic surface and contain polar functional groups. The polyamide-containing ligand (L) will then generally contain a functional grouping reactive with an activated polar group on the polymer. The covalent linkage (A) and the spacer (X) will then be integrated, and may actually be a single linkage, formed by the reaction between the activated polar group from the polymer and the functional group from the ligand and may be represented by Formula 13 below:
xe2x80x83xe2x80x94(CH2)xxe2x80x94(Y)yxe2x80x94(CH2)zxe2x80x94xe2x80x83xe2x80x83Formula 13
where x is 0 or 1; y and z are independently 0 or an integer from 1 to 10; and Y is a functional group or aromatic linkage such as an ether (O), sulfide (S), imine (Cxe2x95x90N), carbonyl (CO), ester (COO), thioester (CSO), amide (CONH), thioamide (CSNH), amine (NH), lower alkylamine (NR), sulfoxide (SO), sulfone (SO2), sulfonamide (SO2NH), phenyl (C6H4), benzyl (CH2C6h4), and the like. At least one of x, y or z must be 1.
The polyamide-containing ligand (L) of the present invention is meant to include any ligand having three or more functional amide groups (NHC(O)CH2) capable of complexing with the desired metal ions and two or more amine nitrogens separated by at least two carbons. Representative examples of polyamide-containing ligands that have at least three amide groups and two or more amine nitrogens separated by at least two carbons include: ethylene bis(oxyethylenenitrilo)tetraacetic acid (EGTAM), diaza-18-crown-6-tetraamide, ethylenediaminetetraacetamide-N-methylenepropanetetraamine (EDTAAMT), tris(2-aminoethyl)amine pentaamide (TRENPAM), and diethylenetriaminepentaacetamide (DTPAM). This list is intended only to be representative of the possible ligands that may be used, the limiting factor being the presence of at least three amide groups and at least two amine nitrogens separated by two or more carbons. Further variations of these ligands may also be used. For example, tris(2-aminoethyl)amine pentaamide (TRENPAM) may be alkyl or aryl substituted as illustrated in Examples 4B (dimethyl substituted) and 4C (phenyl substituted) respectively.
It is to be emphasized that the present invention does not reside in the discovery of the SSxe2x80x94Axe2x80x94Xxe2x80x94 portion of Formula 9. Rather, it is the discovery that the ion-binding and separation capabilities of the polyamide-containing ligand, when attached to an SSxe2x80x94Axe2x80x94X based solid substrates, are optimized.
As summarized above, the present invention is drawn to a novel composition of matter comprising polyamide-containing ligand molecules covalently bound to solid support materials to form the compounds of Formula 9. However, the invention is also drawn to methods for the preferential separation, removal, and concentration of certain desired metal ions, such as certain transition, post-transition, and alkaline earth metal ions from solution. The solution from which the desired ions may be removed may contain other metal ions or hydrogen ions present at greater concentrations than the desired ions. For example, Cd2+, Pb2+, and Ag+ may be removed from acidic and or highly chelative matrices and Ni2+, Co2+, Fe3+, Cu2+ and Ca2+ may be removed from slightly acidic to neutral pH matrices and from chelating matrices.
Moreover the above described ligands covalently bonded to solid supports as shown in Formula 9 provide a means for separating ppb to ppm levels of Cd2+ and Pb2+ from concentrated acid solution by using the separation techniques and equipment generally known in the art.
The method for separating and recovering desired ions is accomplished by forming a complex of the desired ions with a polyamide-containing ligand bonded to the solid supports. Specifically, this is accomplished by flowing a source solution containing the desired ion(s) through a column packed with polyamide-containing ligands bonded to the solid supports in order to complex or chelate the desired metal ion(s) to the polyamide ligand portion of the structure shown in Formula 9. Subsequently, the desired cation which is bound to the polyamide-containing ligand is released by flowing a complex-breaking receiving liquid in much smaller volume than the volume of source solution originally passed through the column. This removes and concentrates the desired ions in the receiving liquid solution by either (a) forming a stronger complex with the desired transition, post-transition or alkaline earth metal ion(s) than does the polyamide-containing ligand, or (b) temporarily forming a stronger interaction with the polyamide-containing ligand than does the desired metal ion(s), and thus, the desired metal ion(s) are quantitatively stripped from the polyamide-containing ligand solid support compound in concentrated form in the receiving solution. The recovery of a desired metal ion(s) from the receiving liquid is accomplished by evaporation, electrowinning, precipitation, or by other known methods.